Many systems such a video games, microwave ovens, telephones and the like incorporate control panels which are hand operated. In some instances, video games utilize a lever, known as a "joystick", to move or guide images displayed on a screen. In other instances, devices such as the microwave oven must be preset to determine cooking times and temperatures as well as other functions.
Various types of controls have been utilized to permit regulation of these types of devices. For instance, with video games, the joysticks comprise a vertically extending rod which can be moved in various directions to cause a like movement of an image on the video screen. In the instance of microwave ovens, various heat sensitive, capacitance or pressure sensitive switches are provided for touching to indicate the functions desired. The pressure sensitive switches require a certain force to be exerted before they are operated. Additionally, they require the mechanical movement of at least some component which movement can lead to failure.
Temperature sensitive switches are frequently slower to react because of the necessity to detect a temperature change. Capacitive activated switches, on the other hand, do not require the physical movement of any part and therefore are more mechanically reliable. However, some capacitive switch systems require rather elaborate circuitry to detect the presence of the operator's finger on or adjacent to the touch plate and sometimes are slow to react. One type of capacitive touch activated switch is shown in U.S. Pat. No. 4,103,252, Capacitive Touch-Activated Transducer System Including a Plurality of Oscillators, issued on July 25, 1978. In this system a plurality of oscillators are utilized with the frequency of the oscillator associated with a touch plate that is touched, being changed and detected. In this system the oscillators exhibit some inertia and resist change and also the oscillators must be permitted to cycle several times before an accurate measurement can be made.
It is the purpose of the present invention to provide an improved touch sensitive system utilizing capacitive type plates which are touched to cause a circuit to generate output signals responsive to that touch.